Abstract:

An imaging system including an image receiving structure including a
tunable-resistivity material; and an energy source to emit an energy beam
at the image receiving structure to pattern-wise program the
tunable-resistivity material. A resistivity can be pattern-wise changed.
Marking material can be pattern-wise adhered in response to the
pattern-wise changed resistivity.

Claims:

1. An imaging system, comprising:an image receiving structure including a
tunable-resistivity material; andan energy source to emit an energy beam
at the image receiving structure to pattern-wise program the
tunable-resistivity material.

2. The imaging system of claim 1, wherein:the image receiving structure
comprises a plurality of electrodes; andthe tunable-resistivity material
is electrically connected to the electrodes.

3. The imaging system of claim 2, wherein:the image receiving structure
further comprises a substrate;the electrodes are disposed over the
substrate;a thermally insulating layer is disposed between the
electrodes; andthe tunable-resistivity material is disposed over the
electrodes and the thermally insulating layer.

4. The imaging system of claim 3, wherein at least one electrode
comprises:a first portion having a first width; anda second portion
having a second width greater than the first width;wherein the first
portion is in direct contact with the tunable-resistivity material.

5. The imaging system of claim 2, further comprising:a first electrode of
the plurality of electrodes;a second electrode of the plurality of
electrodes; andan outer layer disposed over the first and second
electrodes;wherein the tunable-resistivity material is disposed between
the first electrode and second electrodes, and disposed under a
depression in the outer layer.

6. The imaging system of claim 1, further comprising a power supply
configured to supply current only to less than all of the
tunable-resistivity material at any one time.

7. The imaging system of claim 1, wherein the image receiving structure
comprises:a first electrode; anda second electrode over the first
electrode;wherein the tunable-resistivity material is disposed between
the first electrode and the second electrode.

8. The imaging system of claim 1, further comprising:a second energy
source to set resistivity across a portion of the tunable-resistivity
material to be substantially uniform.

9. The imaging system of claim 1, wherein the image receiving structure
comprises:a conductive substrate;an insulating material disposed over the
conductive substrate; andan electrode disposed over the insulating
material;wherein the tunable-resistivity material is electrically
connected to both the conductive substrate and the electrode.

10. The imaging system of claim 1, further comprising:a conductive
substrate;an insulating material disposed over the conductive substrate;
anda plurality of tunable-resistivity cells, each tunable-resistivity
cell including:an opening in the insulating material;a conductive layer
having an edge offset from an edge of the opening; andwherein the edge of
the conductive layer is substantially equidistant from the edge of the
opening and the tunable-resistivity material is disposed between the edge
of the conductive layer and the edge of the opening.

11. The imaging system of claim 1, wherein the tunable-resistivity
material has a bi-stable resistivity.

12. A method of transferring marking material, comprising:pattern-wise
changing an electrical resistivity of a first material; andpattern-wise
adhering the marking material in response to the electrical resistivity
of the first material.

13. The method of claim 12, wherein pattern-wise changing the electrical
resistivity of the first material comprises:irradiating the first
material with a pattern-wise modulated energy beam.

14. The method of claim 12, wherein pattern-wise changing the electrical
resistivity of the first material comprises:pattern-wise changing a phase
of the first material.

15. The method of claim 14, wherein pattern-wise changing the phase of the
first material comprises pattern-wise changing the phase of the first
material between a first phase having a first resistivity and a second
phase having a second resistivity different from the first resistivity.

16. The method of claim 12, wherein pattern-wise adhering the marking
material in response to the electrical resistivity of the first material
comprises:pattern-wise heating the marking material depending on the
electrical resistivity of the first material.

17. The method of claim 16, further comprising:applying current to the
first material to pattern-wise heat the first material;pattern-wise
heating an image receiving structure with the heat from the first
material;contacting the image receiving structure with the marking
material from a donor structure; andpattern-wise separating the marking
material from the donor structure.

18. The method of claim 16, wherein pattern-wise adhering the marking
material in response to the electrical resistivity of the first material
comprises:applying a voltage between a first electrode and a second
electrode;wherein the first material is electrically connected to the
first electrode and the second electrode.

20. The imaging system of claim 19, further comprising:a donor structure
to place marking material in contact with the image receiving structure;
anda brush to contact one of the electrodes when the tunable-resistivity
material coupled to that electrode is adjacent the marking material in
contact with the image receiving structure.

21. The imaging system of claim 19, further comprising:an energy source to
pattern-wise program the tunable-resistivity material in a region of the
image receiving structure prior to contacting the region of the image
receiving structure with the marking material.

Description:

[0002]Printing technologies fall into two distinct groups: those that are
digital and allow every printed page to contain variable text and images
and those that are master plate based and allow high volume duplication
of a single image. Common examples of digital printing technologies
include inkjet, electrophotography (EP), and thermal transfer. Common
examples of master based duplications technologies include offset
lithography, flexography, and gravure.

[0003]Unfortunately, all of the digital printing technologies are severely
limited in speed as compared to the master based duplication processes.
This speed limitation reduces their productivity and fundamentally limits
their economics to copy run lengths no larger than a few hundred copies.
In the case of inkjet printing, the marking inks consist of very dilute
pigments or dyes in a solvent carrier and print speed is limited by the
energy require for solvent evaporation. In the case of
electro-photography, print speed is limited by the energy required for
toner fusion. Finally, the print speed for thermal transfer is limited by
the energy that is required to transform inked material on a ribbon from
either a solid into a liquid or for the case of dye diffusion thermal
transfer (D2T2), the energy from a solid to a gas. A large amount of
energy is required for these thermal methods because the ink must be
raised above a phase change temperature and the latent heat of melting or
evaporation must be delivered. In addition to these considerations, the
lower pigment concentration of typical digital marking materials can lead
to higher marking pile height or image bleed. This is undesirable in
terms of gloss uniformity, tactile feel, stacking thickness for books,
and fold fastness. Furthermore, each of the digital marking materials
usually has a much stricter limitation on color gamut and substrate
latitude and size when compared with offset lithography.

[0004]In waterless offset technologies, a patterned polydimethylsiloxane
(PDMS) layer, commonly referred to as silicone, is used to block the
transfer of ink. That is, silicone is used to prevent the transfer of the
ink. Under the rapid shearing forces of the NIP, the viscoelastic
cohesive forces within the ink can exceed the surface adhesion force at
the silicone interface and the ink is rejected from the non-image areas
of the cylinder. In non-silicone regions the adhesive forces overcome the
built-in cohesive forces of the ink and the ink film splits apart thus
leaving behind a layer of ink in the imaging areas.

[0005]In most offset printing systems, the mass ratio of ink film
splitting in these imaging areas such as between the imaging plate and
the offset blanket is usually a faction between 30/70 and 50/50. In
practical terms, this means that roughly 10 blank pages are needed to
remove enough ink so that the previous image is no longer visible. This
is not a problem when running long jobs because much of the make ready
paper is used to tune the color and alignment of colors on a page so no
additional cost is of concern. This is an issue when variable data is
introduced because ghosting can result from the remaining ink from a
prior image.

[0006]There have only been a few attempts at high quality high speed
variable data digital printing with higher pigment concentration inks.
Gravure and flexography inks with viscosities in the range of 50-1000 cp
have been shown to respond to electrostatic pulling over short distances.
However, the electrostatic forces are too weak to work with high
viscosity high pigment concentration offset inks with viscosities above
100,000 cps.

[0007]Currently, these issues make it incredibly challenging to print
highly viscoelastic marking materials such as offset or waterless offset
inks (i.e. marking materials having dynamic viscosities of
10,000-1,000,000 cps) in a digital fashion with variable data on each and
every page.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a diagram illustrating an imaging system having a
tunable-resistivity material according to an embodiment.

[0009]FIG. 2 is a block diagram of an example of a connection to the
tunable-resistivity material of FIG. 1.

[0010]FIG. 3 is a diagram illustrating a layout of electrodes on an image
receiving structure according to an embodiment.

[0011]FIG. 4 is a cross-sectional view of the image receiving structure of
FIG. 3.

[0012]FIG. 5 is a diagram illustrating a layout of electrodes on an image
receiving structure according to another embodiment.

[0013]FIG. 6 is a cross-sectional view of an example of the image
receiving structure of FIG. 5.

[0014]FIG. 7 is a plan view illustrating examples of tunable-resistivity
cells on the image receiving structure of FIG. 6.

[0015]FIG. 8 is a diagram illustrating an imaging system having a
tunable-resistivity material according to another embodiment.

[0016]FIG. 9 is a diagram illustrating an imaging system having a tunable
energy transfer characteristic according to another embodiment.

[0017]FIG. 10 is a cross-sectional view of a nip according to an
embodiment.

[0018]FIG. 11 is an isometric view of heat dissipation in the marking
material in FIG. 10.

[0019]FIG. 12 is a cross-sectional view illustrating an example of
pattern-wise heating of marking material according to an embodiment.

[0020]FIG. 13 is a cross-sectional view illustrating an example of
pattern-wise heating of marking material according to another embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021]Embodiments will be described with reference to the drawings.
Embodiments allow the formation of a pattern-wise image by selective
heating of marking material in the nip between the donor and image
receiving structures.

[0022]A siloxane, such as silicone, also referred to as
polydimethylsiloxane (PDMS), normally repels viscoelastic marking
materials. Viscoelastic marking materials include waterless offset inks
that are currently used in short run offset presses such as the
Heidelberger Quickmaster or the KBA Metro. Viscoelastic marking materials
are different from most marking materials in that they have a complex
elastic modulus where both elasticity and viscosity (i.e. G' and G'')
both play a substantial roll in determining the marking material
rheology.

[0023]The internal cohesive energy of these marking materials can be made
much larger than the adhesion energy to the surface of silicone. As a
result, the marking materials can be removed off of a silicone surface
with near 100% efficiency. However, by heating such marking materials,
their viscosity and internal cohesive forces (or tack) can temporarily be
lowered enough to allow them to pattern-wise adhere to a silicone
surface. Once on the silicone, such images can be transferred with near
100% efficiency to almost any substrate as long as the substrate has
higher adhesion strength than the silicone. As a result, a non-ghosting
variable data offset transfer process can be realized using waterless
offset inks or other viscoelastic marking materials.

[0024]While waterless offset inks generally do not stick to silicone, if
these inks are heated above their intended temperature range for use,
these inks will readily stick to a silicone layer. In some cases as
little as about 40 degree temperature rise allows the waterless ink to go
from a condition of 0% transfer coverage on to silicone to a full solid
coverage transfer to a silicone surface. One of the reasons that
waterless offset systems must control the temperature to within a few
degrees is to overcome such effects which can sometimes lead to the over
toning of plates due to friction associated heating. Although this effect
is undesirable in some applications, it can be used advantageously to
transfer marking materials in a digital fashion. Moreover, the energy
needed to change a marking material by as little as about 40 degrees can
be less than the energy needed to induce a phase change in the marking
material.

[0025]In an embodiment, a latent electrical resistive layer can be formed
in an image receiving structure. This electrically resistive layer can be
optically or electrically heated and transformed from a high impedance or
low impedance electrical state. One class of such materials known as
phase change materials usually consist of many different binary,
tertiary, or quaternary chalcogenide alloys such as Ge2Sb2Te5 having low
melting points and high crystallization speeds. Such alloys can be used
in DVD and R/W CD ROMS. Because the thickness of such layers are only a
few hundred angstroms, they can be repeatedly switched between amorphous
and crystalline states with low power semiconductor lasers in the range
of only 1-10 mW; In comparison, this is much less power than is needed to
directly heat marking materials in thermal transfer printing
technologies. Once a latent resistive image has been formed, a constant
electrical voltage can be applied across the resistive layer to deliver
an image wise thermal pattern that is no longer limited by row-to-row
line based heating and without the need of high speed high current
electronic drivers.

[0026]An embodiment can be applicable to various novel printing concepts
that use printing of high viscosity marking materials such as variable
fountain solution patterning of offset inks, variable thermal tack
transfer printing of waterless offset inks, pattern-wise tacking of
toner, and variable thermal shooting of front loaded inks, or more rapid
printing using existing thermal transfer technologies.

[0027]FIG. 1 is a diagram illustrating an imaging system 8 having a
tunable-resistivity material according to an embodiment. In this
embodiment, an image receiving structure 10 includes a
tunable-resistivity material 12. An energy source 16 is configured to
emit an energy beam 18 at the image receiving structure 10 to
pattern-wise program the tunable-resistivity material 12. A power supply
23 is configured to provide current to the tunable-resistivity material
12.

[0028]In an embodiment, the imaging system 8 includes a donor structure
22, an image receiving structure 10 to receive marking material in an
image-wise manner, and an energy source 16. The image receiving structure
10 is defined as the structure having a surface onto which an image of a
layer of marking material is first formed and then transferred to a
substrate 28. The image receiving structure 10 can include materials
forming the tunable-resistivity material 12 deposited over a supporting
substrate 9. In the embodiment shown in FIG. 1 this supporting substrate
9 includes a transparent hollow drum.

[0029]The image receiving structure 10 can be a multi-layer surface. The
image receiving structure 10 can include an outer marking material
receiving layer 13. The outer layer 13 is made from a material which
selectively allows the marking material to stick to it when the marking
material is sufficiently changed in viscosity or tack due to an image
wise change in temperature. As discussed earlier, in an embodiment, this
outer layer 13 could be made from a siloxane such as silicone which can
selectively allow transfer onto this layer if waterless offset inks are
heated. In another embodiment, the outer layer 13 can be formed of
Poly(Nisopropylacrylamide), side chain liquid crystal polymers, or other
materials which can change their surface adhesion and dynamic wetting
properties with the application of energy.

[0030]In an embodiment, the outer layer 13 is disposed over the
tunable-resistivity material 12. However, the functional material making
up the tunable-resistivity material 12 could also be incorporated into
the outer layer 13. For example, the tunable-resistivity material 12 can
be formed by a dispersion of nanoparticle material in the outer layer 13
if the nanoparticle material does not greatly change the surface wetting
properties of the outside surface of the outer layer 13. Under this
arrangement the tunable-resistivity material 12 and image receiving
structure 10 can be realized in one layer of coated material.

[0031]The donor structure 22 is configured to receive a substantially
uniform layer of marking material. Forming rollers, anilox rollers,
doctor blades, or the like can all be used to form the marking material
on the donor structure 22. In this embodiment, a substantially uniform
layer of marking material is desired. Thus, any forming, conditioning, or
the like to create such a layer of marking material can be used. As a
result, when the marking material enters a nip 11 as the donor structure
22 moves, a substantially uniform layer of marking material enters the
nip 11.

[0032]As described above, viscoelastic waterless offset inks can be used
as marking materials. However, a marking material is not limited to inks.
Marking materials can be any material that has variable internal cohesive
characteristics. In particular, any material that has internal cohesive
characteristics that decrease when an amount of heat is applied can be
used as a marking material. For example, marking materials can include
highly viscoelastic gel materials, viscoelastic wax based materials, low
melt toners, hot melts such as those used for laminating or gluing boxes
along a seam, or any other highly non-linear viscoelastic marking
materials. In particular, the variable data patterning of hot melt glue
seams is an interesting application that may allow for much higher
through put than a vector scanning glue nozzle based system.

[0033]The power supply 23 can be any variety of circuitry that can supply
current to the tunable-resistivity material. For example, the power
supply can be an alternating current (AC) power supply, a direct current
(DC) power supply, a switched power supply, a linear power supply, or a
combination of such power supplies. The power supply 23 can, but need not
supply power to all of the tunable-resistivity material. As will be
described in further detail below, the power supply can be configured to
supply current only to less than all of the tunable-resistivity material
at any one time.

[0034]In an embodiment, the power supply 23 can be configured to supply
power to the tunable-resistivity material through an electrical inductive
technique. For example, a high frequency induction coil, a series of
coils, or the like can be used to induce a current in the
tunable-resistivity material. The power supply 23 can be formed from such
coils disposed to induce current in the tunable-resistivity material 12.

[0035]As used in this disclosure, an energy source 16 is any device,
apparatus, system, or the like that can emit thermal energy, microwave
energy, optical energy, or the like. For example, the energy source 16
can include heating elements, masers, lasers, or the like. In another
embodiment, a raster optical scanning (ROS) systems with multiple rows of
independently addressed semiconductor lasers can be used as an energy
source to increase the data ripping speed. In an embodiment, the energy
source 16 can be a high power LED array situated outside the image
receiving structure 10. In another embodiment, the energy source 16 can
be a raster scanned high power diode laser.

[0036]Although the energy source 16 is illustrated as outside of the image
receiving structure 10, the energy source 16 can be disposed wherever it
can pattern-wise tune the tunable-resistivity material 12. For example,
the energy source 16 can be disposed within the image receiving structure
10. Accordingly, the energy beam 18 can pass through the substrate 9 of
the image receiving structure 10 to tune the tunable-resistivity material
12.

[0037]To pattern-wise tune the tunable-resistivity material 12, the energy
source 16 can be pattern-wise modulated. The pattern-wise modulation can
be any kind of modulation. Amplitude modulation, frequency modulation,
on-off modulation, direct modulation, external modulation, or the like
can be used. For example, one or more lasers such as fiber lasers,
semiconductor lasers, or the like can be scanned across the across the
tunable-resistivity material 12 to transform portions into different
resistivity states. The intensity, duty cycle, or the like of the energy
source 16 can be modulated to obtain such different resistivity states.
As a result, the tunable-resistivity material 12 can be tuned between a
low resistivity state and a high resistivity state.

[0038]Using the tuned material 12, marking material can be selectively
transferred to the image receiving structure 10 based upon imaging wise
heating. As described above, the energy source 16 is used to pattern-wise
tune the resistance of the tunable-resistivity material 12. The marking
material can be provided on a donor structure 22. The power supply 23
supplies energy to the tuned material 12. Such energy can be applied when
the image receiving structure 10 with the tuned material 12 is in contact
with the marking material on the donor structure 22. Since the
resistivity is pattern-wise tuned, the image receiving structure 10 can
be pattern-wise heated. As described above, the adhesion of the marking
material to the image receiving structure can be related to the
temperature of the marking material. By pattern-wise heating the image
receiving structure 10, marking material is pattern-wise heated.
Accordingly, marking material is pattern-wise transferred as the image
receiving structure 10 separates from the marking material on the donor
structure 22. Accordingly, patterned marking material 24 remains on the
image receiving structure 10.

[0039]A substrate 28 can be brought in contact with the image receiving
structure 10. For example, an impression roller 26 can contact the
substrate 28 to the image receiving structure 10. As the patterned
marking material 24 is moved to contact the substrate 28, the patterned
marking material 24 can cool, increasing its internal cohesiveness. As a
result, its adhesion to the image receiving structure 10, in particular
to a surface of the outer layer 13, is reduced. Patterned marking
material 30 is then transferred to the substrate.

[0040]As described above, a silicone surface is normally used to repel
marking materials. By pattern-wise increasing the adhesion to transfer
the marking materials to the image receiving structure 10, then cooling
the marking materials to reduce the adhesion, an efficient transfer of
marking materials to the substrate 28 approaching 100% can be achieved.
Although the patterned marking materials 24 have been described as being
cooled prior to being transferred to the substrate 28, as long as the
adhesion of the patterned marking materials 24 to the substrate 28, even
in their lower internal cohesion state, is greater than the adhesion to
the image receiving structure 10, the pattern marking materials 24 can be
efficiently transferred. In an embodiment, electronic and lithographic
patterning of the image receiving structure 10 is not required.

[0041]In an embodiment, the marking material did not undergo a phase
transition from a solid to a liquid state. In contrast, the marking
material remained in a viscoelastic state even though the applied heat
lowered the viscosity of the marking material by increasing its
temperature. That is, an amount of energy was transferred to the marking
material sufficient to change its viscosity, but insufficient to change
its phase. This does not mean that the energy transferred must be limited
to less than that which would induce a phase change. In contrast, the
tunable-resistivity material 12 can be similarly used to pattern-wise
heat the marking material to induce a phase change.

[0042]As described above, the adhesion of the marking material to the
image receiving structure 10 is changed. In addition, the internal
cohesiveness of the marking material can be changed. That is, by heating
the marking material, the internal cohesiveness decreases relative to the
adhesion of the marking material to the image receiving surface 10. As a
result, when the marking material exits from the nip 11, marking material
can adhere to the image receiving surface as the internal cohesion is
overcome.

[0043]In an embodiment, the adhesion of the marking material to the image
receiving surface can be affected by a change in the affinity of the
outer layer 13 of the image receiving surface. For example, as the outer
layer 13 is heated, the oleophillic, hydrophilic, or other similar nature
can change in response to heat. Accordingly, a change in the adhesion of
the marking material to the image receiving surface 10 whether due to
changes in the marking material of the image receiving surface 10, a
change in the internal cohesiveness of the marking material, a
combination of such changes, or the like can be used to facilitate the
transfer of marking material to the image receiving surface 10.

[0044]In an embodiment, the power supply 23 can apply a voltage to the
tunable-resistivity material 12 to pattern wise heat the material. For
example, assume that there is a 1:100 ratio of resistances of tuned
states of the tunable-resistivity material 12. Accordingly, when the same
voltage is applied, there will be a 100:1 ratio of power dissipated in
the tunable-resistivity material 12.

[0045]In an embodiment, once the energy source 16 has finished forming
tuning the resistivity of the tunable-resistivity material 12 on the
image receiving structure 10, selective electrical heating can be
accomplished near the nip 11 using the power supply 23. As will be
described in further detail below, the voltage drop due to electrical
resistance along the electrodes coupled to the tunable-resistivity
material 12 can be lower than the voltage drop across the
tunable-resistivity material 12 regardless of its state. Accordingly,
more energy can be directed towards the pattern-wise programmed material
to concentrate the heat in the programmed regions.

[0046]As described above, the image receiving structure 10 is pattern-wise
heated. The image receiving structure with the pattern-wise tuned
material 12 can be brought in contact with marking material on the donor
structure 22 in the nip 11. As a result, the marking material is pattern
wise separated from the donor structure 22.

[0047]In embodiment, a second energy source (not illustrated) can be used
to change the tunable-resistivity material 12 into particular resistance
state. That is, at a point after the patterned marking material 24 has
been transferred to the image receiving structure 10, the second energy
source can tune the resistivity of the tunable-resistivity material 12 to
substantially the same state. For example, after the patterned marking
material 24 has been transferred to the substrate 28, the
tunable-resistivity material 12 can be tuned to substantially the same
state. Moreover, such a second energy source can apply the energy at any
time and/or location between the heating of the tunable-resistivity
material 12 in the nip 11 to before the tunable-resistivity material 12
is programmed with a different pattern by the energy source 16. Prior to
being programmed by the energy source 16, the second energy source can
erase latent resistive image in the tunable-resistivity material 12.

[0048]Although a separate energy source has been described for erasing the
tunable-resistivity material 12, the erasing can be performed by the
energy source 16. For example, the modulation of the energy beam 18 from
the energy source 16 can be appropriately configured to heat the
tunable-resistivity material 12, and then control the modulation of the
energy source 16 over different portions of the tunable-resistivity
material 12 to induce different resistivities.

[0049]FIG. 2 is a block diagram of an example of a connection to the
tunable-resistivity material of FIG. 1. In this embodiment, phase change
material 32 represents a section of the tunable-resistivity material 12.
The phase change material 32 is covered by the outer layer 33 similar to
the outer layer 13 of FIG. 1. FIG. 2 represents the relationship of
structures in the nip 11 of FIG. 1. Thus, marking material 35 contacts
the outer layer 33 and the donor structure 37. The donor structure
represents a part of the donor structure 22 of FIG. 1.

[0050]The phase change material 32 is connected between electrodes 30 and
34. A voltage can be applied between electrodes 30 and 34. Accordingly,
an amount of heat 39 will be dissipated in the phase change material 32
according to its resistivity and at least a portion will propagate to the
outer layer 33 and the marking material 35.

[0051]In an embodiment, the phase change material 32 can be tunable
between bi-stable electrical states meaning the phase change material 32
can be capable of being switched back and forth many times without
reliability issues. In addition, the phase change material 32 can have
fast switching speeds, for example, at about 10 nanoseconds, which can
result in a data rate of about 100 Mbits/s. The energy source 16 can be
modulated at such speeds to tune the phase change material 32. For
example, an optical raster output scanning (ROS) laser diode system can
be modulated as such speeds to be used as the energy source 16.

[0052]Examples of materials having such tunable-resistivity
characteristics are chalcogenide materials used in RW-CDs and RW-DVDs and
vanadium dioxide (VO2) used for high speed photochromic switching. For
example, the phase change material 32 can include any chalcogenide
binary, tertiary, or quaternary semiconductor alloy capable of being
switched between high and low electrical resistive states. Binary
chalcogenide materials that can exhibit resistive switching memory
include materials such as GexTey, GaxTey, InxTey, GexTiy, InxSby, InxSey,
SbxTey, GaxSby, GexSby, and SexSby. x and y refer to the proportional
amounts of each element. In some materials, x and y combined account for
close to 100% of the composition. In other materials, dopants of one or
more other elements can be present. Tertiary chalcoginide materials that
can exhibit resistive switching memory include InxSbyTez, InxSbySez,
InxSbyGez, InxSbyGaz, GexSbyTez, GexSbySez, SexSbyTez, GexSeyTez,
InxSbyTez, where x,y, and z operate similarly to x and y above.
Quaternary chalcoginide materials that can exhibit resistive switching
memory include AgInSbTe, SiGeSbSe, in any compositional amount.

[0053]In another example. The phase change material 32 can be any metallic
oxide material known to exhibit stable electrical switching states. For
example, such phase change metallic oxides can include Nb2O5, Al2O3,
Ta2O5, TiO2, NiO, SrTiO3, ZrO2, or any other compositional variation of
these alloys.

[0054]Some of these materials have shown repeatable bi-stable switching
properties with low energy diode lasers over many billions of cycles. It
should be noted that one of the most popular chalcogenide materials today
is the so called GST material which is very close in chemical formulation
to Ge2Sb2Te5 and can be used for this application. Both the GST and VO2
materials can change their resistivity over several orders of magnitude
in response to laser heating. For example, the resistivity of some phase
change electrical materials in the polycrystalline state can range
between about 0.01-1.0 Ohm-cm and a resistivity in the amorphous state is
between about 100-1E5 Ohm-cm.

[0055]In addition, both resistivity states can exist as relatively thin
layers in the range of about 10-100 nm thick and both exhibit hysteretic
dramatic changes in electrical properties that can be optically
programmed by heating them up and cooling them down according to
particular laser modulation methods. Moreover, the relative thinness
results in a reduced amount of energy to change their phase allowing for
lower power energy sources such as diode lasers, and/or higher throughput
when tuning the resistivity.

[0056]In an embodiment, the energy source 16 can be controlled to melt the
phase change material 32 and allow it to re-solidify into an amorphous
state. As a result, a high resistance will be present and a reduced
amount of local heating will be induced. For example, a laser can be
pulsed at a repetition rate less than about 10 nanoseconds with a high
laser power.

[0057]The phase change material 32 can be recrystallized into a
polycrystalline state to set the resistivity to a lower level. For
example, the energy source 16 can apply continuous laser energy at a
lower energy state. Phase change materials as described above have been
designed so that the recrystallization times, given sufficient power, can
be on the order of 10-100 ns.

[0058]In an embodiment, when using a bi-stable phase change material 32,
the tunable-resistivity material 12 can have a bi-stable resistivity.
Pattern-wise changing the phase of the tunable-resistivity material 12
can include pattern-wise changing the phase of the tunable-resisitivity
material 12 between a first phase having a first resistivity and a second
phase having a second resistivity different from the first resistivity.

[0059]In an embodiment, layers of the image receiving structure 10 can be
selected to be substantially transparent to the energy beam 18 from the
energy source. In addition, the layers can be selected to have refractive
index matching properties to reduce reflections. Accordingly, energy
transfer to the tunable-resistivity material 12 can be increased. In
addition, one or more layers of the image receiving structure 10 can act
as a passivation layer that does not allow the tunable-resistivity
material 12 to migrate or diffuse into surrounding layers.

[0060]In addition, the layers can be selected to be able to handle the
thermal diffusion from the tunable-resistivity material 12. For example,
a layer can be selected having a lower thermal conductivity. As a result,
heat needed to change a phase of the tunable-resistivity material 12 can
be reduced as less heat escapes into the surrounding layers.
Alternatively, layers can be selected with higher thermal conductivity.
Accordingly, when particular programmed regions of the
tunable-resistivity material are energized, the resulting heat can be
efficiently transferred to the marking material. In an embodiment, a
dielectric layer composed of mixture of ZnS(80%)-SiO2(20%) can
satisfy such of requirements for a wide variety of chalcogenide phase
change materials.

[0061]FIG. 3 is a diagram illustrating a layout of electrodes on an image
receiving structure according to an embodiment. The embodiment includes
an image receiving structure 43 including a tunable-resistivity material
56; and multiple electrodes coupled to the tunable-resistivity material.
Tunable-resistivity material 56 represents material that is electrically
connected to electrodes 38, 40, 42, and 44. Brushes 36 and 46 can be used
to contact the electrodes.

[0062]In an embodiment, the image receiving structure 43 can be a drum.
FIG. 3 can represent a top view of a portion of the cylindrical surface
of the drum. The brushes 36 and 46 can be disposed such that as the drum
rotates, each of the electrodes of the drum rotates to be in contact with
a corresponding one of the brushes 36 or 46. For example, in FIG. 3,
brush 46 is illustrated as contacting electrode 40. However, as the drum
rotates, electrode 44 can be brought into contact with brush 46.

[0063]Although a drum has been given as an example of the image receiving
surface 43, any shape can be used. For example, any shape, such as a belt
configuration, that allows the brushes 36 and 46 to contact the
electrodes 38, 40, 42, 44, and any other electrodes can be used. In
addition, although only one electrode has been illustrated as being
coupled to a brush at one time, a single brush can contact multiple
electrodes. For example, brush 36 can be sized to contact electrodes 36
and 42 simultaneously. As a result, multiple rows of the
tunable-resistivity material 56 can be heated at any one time.

[0064]In an embodiment, a raster optical scanning system can follow the
electrodes such that changes to the resistivity can be induced in the
region between these lines. An optical reflective feedback system can be
used to center the lasers and provide tracking feedback. In another
embodiment, endpoint patterns at the edges of the image receiving
structure 10 can also provide feedback.

[0065]FIG. 4 is a cross-sectional view of an image receiving structure
according to an embodiment. The cross-section of FIG. 4 is along line 45
of FIG. 3. Referring to FIGS. 3 and 4, in this embodiment, a dielectric
59 is disposed on a substrate 48. Electrodes 38, 40, 42, and 44 are
disposed on the dielectric 59. Heating can be accomplished by passing
current between the brushes 36 and 46. Accordingly, current can flow
through electrodes 38 and 40, and the tunable-resistivity material 56
between electrodes 38 and 40.

[0066]Electrodes 38, 40, 42, and 44 of FIG. 3 or FIG. 4 can be any variety
of conductive materials. For example, metallic materials of can include
copper, aluminum, or the like, which have relatively low intrinsic
resistivity, can be used. Moreover, such metallic materials can act to
thermally isolate adjacent pixels of the tunable-resistivity material 56
by redirecting the lateral spread of thermal energy downward towards the
substrate 48 which serves as an electrical and thermal ground plane. For
example, if the tunable-resistivity material 56 in region 49 is heated,
that heat could migrate to region 51. However, since electrode 54 can
have a higher thermal conductivity, migrating heat can be directed into
the electrode 54 rather than region 51 and any marking material
contacting region 51. Accordingly, a stable high resolution thermal image
can be formed over a longer time period. Thus the tunable-resistivity
material 56 can, but need not be heated line by line. Instead a swath of
the imaging surface can be heated at once. Accordingly, an alignment of
the heated image to the exit of the nip can have a reduced tolerance.
That is, the longer the thermal image maintains its contrast by isolating
the dissipation of the heat, the thermal image can be established both
before the nip, maintained after the exit of the nip, or the like.

[0067]A thermally and electrical insulating layer 53 is disposed between
the electrodes. The thermally insulating layer 53 thermally insulated the
tunable-resistivity material 56 from portions of the electrodes 38, 40,
42, and 44, and the dielectric 59. Accordingly, a reduced amount of heat
from the tunable-resistivity material 56 will be lost to the electrodes
38, 40, 42, and 44, the dielectric 59, the substrate 48, or the like.

[0068]The tunable-resistivity material 56 is disposed over the electrodes
38, 40, 42, and 44 and the thermally insulating layer 53. The
tunable-resistivity material 56 is electrically connected to the
electrodes 38, 40, 42, and 44. In an embodiment, the electrodes 38, 40,
42, and 44 can have portions of varying width. For example, electrode 42
includes a first portion 54 having a first width and a second portion 52
having a second width greater than the first width. The first portion 54
is in direct contact with the tunable-resistivity material 56. The
current that passes through the tunable-resistivity material 56 from
electrode 42 can enter at the connection between the brush 36 and
electrode 42. The larger second portion 52 can provide a low resistivity
path along the length of the electrode 38. The first portion 54 provides
a connection from the low resistivity second portion 52 to the
tunable-resistivity material 56. Since the second portion 54 would carry
substantially only the current to the adjacent region of the
tunable-resistivity material 56, a lower current density passes through
the second portion 54. As a result, the second portion 54 can be made
smaller, yet still have a reduced effect on the voltage drop between the
brushes 36 and 46. Accordingly, current can be efficiently directed to
the tunable-resistivity material 56, and the tunable-resistivity material
56 can be thermally insulated from a majority of the electrodes.

[0069]In an embodiment, such a horizontal arrangement of the
tunable-resistivity material 56 can tolerate defects in the material. For
example, during manufacturing, pinhole defects can be formed in the
tunable-resistivity material 56. Even if such pin holes are present, the
pinholes would be perpendicular to the flow of current. Accordingly, the
pin holes have a reduced effect on the resistivity of the
tunable-resistivity material 56.

[0070]In an embodiment, pixelation of an image can occur due to the
electrodes. For example, since a first current can flow from electrode 38
to electrode 40 along axis 47, heating the tunable-resistivity material
56 through which the current passes. The next different current that can
flow is between electrode 40 and 42 along axis 55. Thus, the resolution
in the direction of axis 47 is limited by the electrode spacing. In
contrast, in axis 57, the resistivity of the tunable-resistivity material
56 can be varied without regard to the electrode spacing. For example, by
directly modulating the laser at a high bandwidth, a high resolution
control can be achieved along axis 57. As a result, a higher effective
pixel density along axis 57 can be achieved. This can allow a higher
resolution, a variable spot width gray scale, or the like to be achieved.

[0071]FIG. 5 is a diagram illustrating a layout of electrodes on an image
receiving structure according to another embodiment. In this embodiment,
the image receiving structure includes a conductive substrate 70 on which
electrodes 60, 62, 64, and 66, and the tunable-resistivity material 80
are formed. A brush 68 can contact the electrodes 60, 62, 64, and 66. The
electrodes 60, 62, 64, and 66 can be used as an electrical connection to
one side of the tunable-resistivity material 80. The other connection is
the conductive substrate 70. That is, current used to heat the
tunable-resistivity material 80 flows between the brush 68 and the
conductive substrate 70.

[0072]FIG. 6 is a cross-sectional view of an example of the image
receiving structure of FIG. 5. The electrodes 60, 62, and 64 are disposed
over an insulating material 74. The insulating material 74 is disposed
over the conductive substrate 70. In this embodiment, the electrodes 60,
62, and 64 include two regions 76 and 78. Region 76 is narrower in width
than region 78; however, it is thicker than region 78. Accordingly,
current can flow through region 76 with less of a voltage drop than
through region 78. Current can be distributed along the length of the
electrode 62 with a reduced voltage drop. The thinner region 78 can be
use to locally distribute current to the tunable-resistivity material 80.
That is, it may not carry as much current as region 76 and can be thinner
without an excessive voltage drop or associated heating.

[0073]Openings 77 and 79 expose the conductive substrate 70. The
tunable-resistivity material 80 can contact the conductive substrate 70
through the openings 77 and 79. Accordingly, current can flow between the
electrodes 60, 62, and 64, and the conductive substrate 70 through the
tunable-resistivity material 80 and the corresponding openings 77 and 79.
An outer layer 82, such as silicone, as described above, covers the
electrodes 60, 62, and 64 and tunable-resistivity material 80.

[0074]In an embodiment, the conductive substrate 70 need not be the entire
substrate for the image receiving structure. For example, the conductive
substrate 70 can be a conductive layer over a non-conductive substrate
for the image receiving structure.

[0075]FIG. 7 is a plan view illustrating examples of tunable-resistivity
cells on the image receiving structure of FIG. 6. In this embodiment, the
outer layer 82 is not illustrated as it can be transparent. In addition,
the tunable-resistivity material 80 is not illustrated as it can be
formed over the entire illustrated surface; however, this does not mean
that the tunable-resistivity material 80 must be formed over the entire
surface. For example, the tunable-resistivity material 80 can be formed
on the electrodes only over the thinner regions 78.

[0076]Referring to FIGS. 6 and 7, in this embodiment, each
tunable-resistivity cell has an opening 88. Similar to the openings 77
and 79, the opening 88 allows electrical contact to the conductive
substrate. Opening 86 is an opening in the electrodes exposing the
insulating material 74. In particular, it is an opening in the thinner
regions 78 of the electrodes.

[0077]The openings 86 and 88 form concentric circles. Accordingly, a
distance from region 78 of the electrodes to the conductive substrate 70
can be substantially similar. As a result, assuming that the
tunable-resistivity material 80 for the cell is programmed with the same
resistivity, the resistance of the cell can be substantially evenly
distributed over the cell.

[0078]Currents 85, 87, and 89 represent some currents that can flow
through a tunable-resistivity cell. Current 85 is the current passing
through region 76 of the electrode 62. Currents 87 represent the current
passing through region 78 to the tunable-resistivity material 80 of the
cell. The resistivity of region 78 can be selected to be substantially
less than the resistivity of the lowest resistivity state of the
tunable-resistivity material 80. Thus, even if a current 87 would travel
a longer path from electrode 62 towards electrode 64, the additional
resistance due to the longer path can still be lower than the lowest
resistivity of the tunable-resistivity material 80. Currents 89 represent
the current distribution through the tunable-resistivity material 80.
Because of the lower resistivity of the regions 76 and 78 of the
electrodes, the current can be substantially evenly distributed over the
tunable-resistivity material 80 of the cell. As a result, heat generated
by the cell can be substantially evenly distributed.

[0079]The resistivity of region 78 of the electrodes can be selected to
localize the current distribution from an electrode. For example, since
electrodes 60, 64, and 66 are electrically connected to electrode 62,
portions of current 85 can flow to those electrodes even if they are not
directly energized. However, as region 78 of the electrodes separate
regions 76, any current passing to other electrodes must pass through one
or more regions 78 of the electrodes. As region 78 is thinner, it can
have a higher resistivity than region 76. Thus, for each subsequent
section of region 78, the total resistance increases, reducing the amount
of current that flows through that section. Accordingly, the resistivity
of region 78 can be selected to both below an amount to substantially
evenly distribute current in a given row of tunable-resistivity cells yet
high enough isolate a number of other rows of tunable-resistivity cells
from the applied current. As a result, the rows of tunable-resistivity
cells that are energized can be controlled.

[0080]Although the region 78 has been described as being electrically
connected between electrodes, the all electrodes need not be electrically
connected. For example, gaps in region 78 can separate one or more
electrodes from other electrodes. Although a circle has been used as an
example, the openings 86 and 88 can have different shapes. Any shapes
such that the resistance of the cell is substantially evenly distributed
can be used. For example, a substantially square shape can be used with
the corners formed to substantially evenly distribute the resistance of
the cell.

[0081]Although the tunable-resistivity cells have been illustrated in a
recto-linear arrangement, the tunable-resistivity cells can be disposed
on the image receiving structure as desired. For example, the
tunable-resistivity cells could be disposed in a hexagonal arrangement.
Accordingly, the electrodes may not be straight as illustrated and could
weave in between the tunable-resistivity cells.

[0082]In an embodiment, the size of a tunable-resistivity cell can be made
smaller than a spot size of the energy beam 18 used to program the
tunable-resistivity material. For example, opening 88 could be about 3
ums in diameter, the opening 86 could be about 9 ums in diameter, and the
cell spacing could be about 12 urns center to center. This can result in
approximately 2400 dpi in density in tunable-resistivity cells.

[0083]With such a cell density and a larger laser spot size, the alignment
of the energy beam 18 to the image receiving structure can, but need not
be as precisely controlled. For example, a laser spot size is about 42
ums or larger, a misalignment of the tunable-resistivity cell pattern to
the sweep of the laser has a reduced impact on image quality. That is, in
this example, the laser spot size is about 3.5 tunable-resistivity cells
in width. Accordingly, a misalignment of a tunable-resistivity cell will
have a reduced impact.

[0084]Although embodiments described above have had the electrodes
substantially aligned in one dimension, the electrodes can be aligned in
multiple dimensions. For example, electrodes can be aligned in two
dimensions across the surface of the image receiving surface.

[0085]In addition, if the laser strays to close to the electrical
connection between the phase change layer and an address line, the
thermal time constant may be impacted due to the high thermal
conductivity of the electrical address lines. Accordingly, the energy
source 16 can includes a feedback controller configured to align the
energy beam 18 to the tunable-resistivity material between the
electrodes. As a result, the impact of the higher thermal conductivity
can be reduced.

[0086]In an embodiment, current can be passed in a direction that is
vertical with respect to the image receiving structure 10. For example,
the image receiving structure can include a first electrode, a second
electrode over the first electrode, and the tunable-resistivity material
disposed between the first electrode and the second electrode. With a
vertically directed geometry, a need for patterning of the image
receiving structure, tracking of the energy beam 18 to the image
receiving structure, or other image receiving structure pattern related
requirements can be reduced or eliminated.

[0087]In such a vertical directed geometry, a pin-hole free coating
schemes can be used. Atomic layer deposition (ALD) processes can be pin
hole free for a few nm layer thickness. This layer can be conformal to a
non-uniform surface. In addition various oxides can be put down with ALD.
For example, Al2O3 can be deposited using ALD to conformally
coat a surface free of pin holes.

[0088]Moreover, the relative distance through the tunable-resistivity
material that current passes to generate heat can be thinner than in a
horizontal tunable-resistivity material application. Accordingly, the
resistivity of the tunable-resistivity material can be selected to be
higher. For example, by adjusting the composition of metal oxide
materials, switching states having higher resistivities than chalcogenide
materials can be created. Such oxides include Nb2O5, Al2O3, Ta2O5, TiO2,
NiO, SrTiO3, and ZrO2.

[0089]In addition, the first electrode and/or the second electrode can be
made transparent to the energy of the energy beam 18. As a result, such
electrodes can be between the energy source 16 and the
tunable-resistivity material, yet the tunable-resistivity material can
still be programmed. In another embodiment, thin conductive layers in a
mesh can be used for the electrodes. For example, a thin metal mesh layer
can have a higher conductivity that some optically transparent materials.
However, the mesh structure can allow an amount of transparency and an
amount of flexibility.

[0090]FIG. 8 is a diagram illustrating an imaging system having a
tunable-resistivity material according to another embodiment. This
embodiment illustrates additional systems that can be part of the imaging
system. Forming rollers 94 can be used to apply marking material to an
anilox roller 96. A doctor blade 98 can shape the marking material on the
anilox roller 96.

[0091]Accordingly, marking material can be metered onto the donor surface
22. In an embodiment, the marking material can be metered using a
`keyless` marking material metering system. Such a marking material
metering system does not require adjustment of the marking material flow
based upon the image coverage area and can be used with waterless marking
materials. The doctor blades 98 and 100 can be used to control the
thickness and uniformity of the marking material. Once a substantially
uniform marking material layer has been formed on the donor surface 22,
the marking material can be rotated into the nip 11 were it can be heated
as described above by energizing the tunable-resistivity material 12.

[0092]A cooling source can cool the patterned marking material 24. For
example, cool air 102 can be directed towards the patterned marking
material 24. As a result, the patterned marking material 24 that was
heated to adhere to the image receiving structure 110 can be cooled to
reduce the adhesion to the image receiving structure 110. Since the
patterned marking material 24 is not in contact with a surface other than
the image receiving structure 110, even with the lowered adhesion, it
will still adhere to the image receiving structure 110. However, when
brought in contact with the substrate 28, the patterned marking material
24 can adhere to the substrate 28. As described above, the marking
material can be removed from a silicone surface with about 100%
efficiency. As a result, a substantial amount of the patterned marking
material 24 is transferred to the substrate 28.

[0093]In an embodiment, an air knife 104 can be used to separate the
substrate 28 from the image receiving structure 110. Although the
adhesion of the patterned marking material 24 to the substrate 28 may be
greater than the adhesion to the image receiving structure 110, the
adhesion of the marking material to the image receiving structure 110 can
cause the substrate 28 to adhere to the image receiving structure 110. In
particular, if the substrate 28 is a single page of paper, for example,
the leading edge of the paper may follow the image receiving structure
110 up towards the cleaning roller 106. Accordingly, the air knife 104
can separate the substrate from the image receiving structure 110.
Alternatively, or in addition, the substrate 28 can be held under tension
to separate it from the image receiving structure 110.

[0094]Although about 100% of the patterned marking material 24 can
transfer to the substrate, some portion can remain. If left on the image
receiving structure 110, the remaining marking material can cause
ghosting in subsequent imaging operations. Accordingly, a cleaning roller
106 and a conditioning roller 108, or the like can be used to prepare the
image receiving structure 110 for subsequent applications of marking
material.

[0095]Although forming rollers, doctor blades, anilox rollers,
conditioning rollers, cleaning rollers, and the like have been described
above, such systems need not be identical to those illustrated in FIG. 8.
In an embodiment, any system that can form a substantially uniform layer
of marking material by the time the marking material is in the nip 11 can
be used. Similarly, any conditioning system that removes marking material
from the image receiving structure 110 can be used.

[0096]In an embodiment, the imaging receiving structure 110 can be a drum.
The drum can be a cylindrical glass drum. The deposition of the
tunable-resistivity material 12 on the cylindrical glass drum can be
performed with drum sputtering systems designed for large area batch
sputtering of flexible substrates. Alternatively, the tunable-resistivity
material 12 can be sputtered on a flexible high temperature compatible
dielectric substrate such as polyimide. Localized annealing at
temperatures at about 440 C can be used to transform the sputtered
amorphous VO2 to a crystalline form that exhibits the change in
energy transfer characteristics.

[0097]FIG. 9 is a diagram illustrating an imaging system having a tunable
energy transfer characteristic according to another embodiment. Although
a drum or a cylinder has been described above as a supporting substrate
for the image receiving structure 10, other supporting substrates can be
used. In this embodiment, the supporting substrate is a belt 61. Rollers
63 can tension the belt 61. As a result, contact with the marking
material of the donor roller 22 is maintained in the nip 11. Patterned
marking material can be transferred to the belt 61 similar to the
transfer to the image receiving structure 10 as described above as
illustrated by patterned marking material 24. The patterned marking
material 24 can then be transferred to the substrate 28 by impression
roller 26.

[0098]The belt 61 can have a cross-section similar to that described with
reference to FIG. 2. However, in this embodiment, the supporting
substrate 36 of FIG. 2 would be material of the belt 61. In an
embodiment, a material of the belt 61 has high strength, high tear and
scratch resistance, low cost, and is optically transparent over the
wavelength range of the energy sources used for heating and/or
patterning. For example, optically clear polyethylene terephthalate can
be used as a belt material as it is transparent over a wavelength range
from about 600 nm-1100 nm.

[0099]The deposition of the mask layer of the belt 61 can be performed
similar to techniques described above. For example, a nanoparticle liquid
suspension of VO2 can be dip coated over the belt. Similar
techniques can be used to apply the outer layer as described above.

[0100]Due to the belt geometry, the space limitations of fitting a laser
raster scanning system, line image projection optics, or the like within
a drum 9 as described above can be alleviated. Routing of the belt 61 can
allow more internal access to the nip region. As a result, first and
second energy sources 16 and 14 can be disposed within the belt 61.

[0101]FIG. 10 is a cross-sectional view of a nip according to an
embodiment. In an embodiment, the energy can be deposited in the nip
region between the donor 118 and image receiving structures 112 such that
the heat does not have time to diffuse. If the heat does have time to
diffuse, the desired image can be washed out. Distance 120 is the
thickness of the outer layer 114 of the image receiving structure 112.
Distance 122 is the thickness of the marking material 116 in the nip. The
thickness 122 is a minimum where the donor structure 118 and image
receiving structure 112 are at their closest at location 109. Arrow 130
indicates a direction of rotation of the image receiving structure 112.
Arrow 134 indicates a direction of rotation of the donor structure 118.
Region 124, where the heat 126 is transferred from the
tunable-resistivity material 128 to the marking material 116, is offset
from location 109. That is, the heat transfer occurs as a location 124
offset from the location 109 where the image receiving structure 112 and
the donor structure 118 are the closest.

[0102]FIG. 11 is an isometric view of heat dissipation in the marking
material in FIG. 10. In this view, a tunable-resistivity material 138 is
illustrated between the substrate 136 and the outer layer 140. This view
illustrates the conduction of heat 154 from the point of application of
energy to the tunable-resistivity material 138.

[0103]Referring to both FIGS. 10 and 11, in an embodiment, for imaging to
occur, the marking material should transfer to the outer layer 140 at the
exit 105 point of the nip 103 in a time period less than the lateral
thermal diffusion time constant or image blurring can occur. Accordingly,
the heat spreading area ΔA can be a fraction of the heated area
with radius 150. In addition, the overall diffusion rate of heat in both
the vertically and lateral directions should not be so fast so as to
allow the marking material to cool down before it has a chance to split
at the exit 105 of the nip 103. Marking material 132 represents marking
material that was heated to transfer it to the image receiving structure
112.

[0104]As the location 124 is moved further away from the exit 105 of the
nip 103, heat will have a longer time to diffuse and the temperature of
the marking material 116 will have a longer time to decrease from its
peak value. Thus, in an embodiment, the location 124 where the
tunable-resistivity material 128 is heated can be disposed close to the
exit 105 of the nip 103. However, if the location 124 is too close to the
nip exit 105 such that the marking material 116 has already partially
lifted off the outer layer 140, then a non-uniform transfer can occur.

[0105]In addition, the marking material 116 can be thinner than the width
of the heated location 124. As a result, splitting dynamics of the
marking material for one pixel can be isolated from the dynamics of
neighboring pixels. Typical waterless offset inks can be put down on
paper in a thickness range of about 0.5 to 1.0 micron. Accordingly, at a
resolution of even 1200 dpi (21 ums spacing), there is still about a 1:20
ratio between the marking material 116 thickness and the nearest neighbor
pixel.

[0106]A time constant for thermal diffusion can be estimated from marking
material parameters. At an imaging resolution of 600 dpi, a heated pixel
region can be on the order of 42 ums in diameter. As described above the
marking material thickness 142 is no more than about a few microns thick.
Because the marking material thickness 142 is much less than the width
150 of the conducted heat, vertical diffusion of heat dominates the
overall cooling time constant. That is, heat diffusion can occur in
directions 146 and 152; however, more heat will be transferred in
directions 148 towards the donor structure 116 or in direction 156
towards the image receiving structure 112.

[0107]The thermal conductivity of the outer layer 140 depends on the
formulation. If a native PDMS material is used without modified
chemistry, the thermal conductivity, KPDMS, is expected to be close to
the range of 0.15-0.2 W/m-K. While the exact specific heat and thermal
conductivity of the marking material 142 vary from one formulation to
another, typical values for waterless offset inks can be used to give
order of magnitude calculations. Typical thermal values for the high
molecular weight oils used in waterless inks are a specific heat
c.sub.ρ˜2000 J/kg-K, a mass density of ρink˜1.0
gm/cc, and a thermal conductivity κink˜0.15 W/m-K. Given
that vertical conduction dominates the loss of heat, the expected thermal
time constant can be estimated from a scaling relation in equation 1:

td=c.sub.ρ*ρink*d2/κPDMS (1)

[0108]d is on the order of the absorption depth thickness of the marking
material in the nip. For the typical values stated, the diffusion time,
td is on the order of 100 us assuming d=2-3 um as the overall
absorption depth. In contrast, the time constant for lateral heat
diffusion through the ink is expected to be on the order of 1 ms due to
the fact the heat has to travel through 42 ums. For print speeds of 100
ppm, the linear feed rate of the printer is on the order of ˜0.5
m/s. This speed results in the heated region 124 being positioned to
within approximately 50 microns of the exit 105 of the nip 103. As the
imaging speed is increased, this requirement can be relaxed somewhat due
to the larger distance over which the structures travel within a given
thermal time constant.

[0109]In an embodiment, the donor structure 118 has a thermal conductivity
less than a thermal conductivity of the marking material 116. For
example, the donor structure 118 can be made out of a low thermal
conductivity material that is compatible with most UV inks. An Ethylene
Propylene Diene Monomer (EPDM) coated roller is can be used with UV
curable inks and with a thermal conductivity in the neighborhood of about
0.3 W/m-K.

[0110]FIG. 12 is a cross-sectional view illustrating an example of
pattern-wise heating of marking material according to an embodiment. The
image receiving structure of FIG. 12 is similar to that of FIG. 4. In
particular, the image receiving structure includes a substrate 158, a
dielectric 160, a first electrode 161 formed of a first portion 164 and a
second portion 162, a second electrode 167 formed of a first portion 165
and a second portion 163, a dielectric 169, a tunable-resistivity
material 166, and an outer layer 168.

[0111]In this embodiment, the tunable-resistivity material 166 has been
tuned to a relatively lower resistivity in region 171 between electrodes
161 and 167. Accordingly, a higher amount of power is dissipated in
region 171. Thermal energy 170 passes through the outer layer 168.
Accordingly, toner particles 174 are tacked to the outer layer 168 while
toner particles 172 outside of region 171 are not. As a result, toner
particles are pattern-wise tacked to the image receiving structure, and
can be transferred to another substrate.

[0112]FIG. 13 is a cross-sectional view illustrating an example of
pattern-wise heating of marking material according to another embodiment.
The image receiving structure of FIG. 13 is similar to that of FIG. 12.
However, the outer layer 176 includes a depression 177. In this
embodiment, the tunable-resistivity material 166 that is between the
electrodes 161 and 167 is disposed under the depression 177.

[0113]Marking material 182 can be deposited in the depression 177. When
thermal energy 178 is transferred to the marking material 182, the
marking material 182 can vaporize in a region 180 adjacent to the outer
layer 176. The pressure of the expanding vapor in region 180 can eject
the marking material 182 in direction 184. A substrate (not illustrated)
can be suitably positioned to receive the ejected marking material. Since
the tunable-resistivity material 166 can be pattern-wise tuned, the
marking material can be pattern-wise ejected on to the substrate.

[0114]In an embodiment, the depression 177 can be a circular depression in
the outer layer 176. The outer layer 176 can have an array of such
circular depressions 177 where each circular depression 177 is associated
with an individually addressable portion of the tunable-resistivity
material 166. Accordingly, from each depression 177, an amount of marking
material can be pattern-wise ejected on to a receiving substrate.

[0115]Although a depression 177 and, in particular, a circular depression
177 in the outer layer 176 has been described, any shape or structure
that can divide the marking material 182 can be used. For example,
different shapes such as square or rectangular depressions, trenches, or
the like can be used.

[0116]Another embodiment includes an article of machine readable code
embodied on a machine readable medium that when executed, causes the
machine to perform any of the above described operations. As used here, a
machine is any device that can execute code. Microprocessors, tunable
logic devices, multiprocessor systems, digital signal processors,
personal computers, or the like are all examples of such a machine.

[0117]Although particular embodiments have been described, it will be
appreciated that the principles of the invention are not limited to those
embodiments. Variations and modifications may be made without departing
from the principles of the invention as set forth in the following
claims.